Using a prospective, open label design in children meeting Rome III childhood IBS criteria, our Specific Aims are to: 1) Characterize the effectiveness of a restricted FODMAPs diet in improving symptoms (number of abdominal pain episodes; primary endpoint); 2) To determine the mechanisms by which a restricted FODMAPs diet may work. We Hypothesize that: 1) A restricted FODMAPs diet will improve abdominal pain symptoms associated with childhood IBS and identified fructose malabsorption; 2) A restricted FODMAPs diet will improve symptoms in part by decreasing bacterial fermentation gas production amongst other potential mechanisms.